Effervescent mixtures made by this invention are used to encapsulate hypochlorite releasing compounds for use in disinfecting as described in co-pending applications xe2x80x9cHalazone Disinfecting Systemsxe2x80x9d, and xe2x80x9cTricalcium Hydrogen Tetraphosphate Buffered Disinfectantsxe2x80x9d and for use in mouthwash preparations as described in co-pending application xe2x80x9cCavity Detecting Mouthwash and Cold Preventionxe2x80x9d.
This invention relates to the manufacture and use of a composition of citric acid and carbonate salt for the production of effervescent products, especially those compatible for use with calcium hypochlorite for use in the disinfecting of water for consumption.
Effervescent tablets have been made to effect the rapid dissolution of drugs and for the production of carbonate beverages. Some years ago a sweetened and flavored tablet that formed a carbonated beverage was sold under the trade name xe2x80x9cFizziesxe2x80x9d. A popular antacid, Alka-Seltzer, uses effervescence to cause rapid dissolution of the active ingredients. The conditions usually employed require only that the effervescence distribute soluble components with the solution. Effervescent tablets are used to improve the cleaning rate for dentures.
The patent to Schobel, et al (U.S. Pat. No. 4,671,972), describes a composition and method of manufacture of tablets suitable for the cleansing of dentures by providing a chlorine odor inactivator. This patent uses dichloro-isocyanurate as the chlorine generator.
The patent to Kurobe, et al (U.S. Pat. No. 4,853,211), describes effervescent compositions for vaginal suppositories which include solid acids, drying agents of the sodium sulfate type, and bicarbonate salts. No oxidizing agents are included. Components are mixed and tableted together. The presence of drying agent reduces swelling on storage of the tablet.
The patent to Goldman and Nathanson (U.S. Pat. No. 4,850,872) describes a method of preparing a tooth for capping which utilizes a chelating agent including citric acid and ethylenediamine followed by flushing with a solution of sodium hypochlorite with surface active agents and emulsifiers.
The prior mixing of citric acid with alkali metal carbonate or bicarbonate to form a granular effervescent mixture is accomplished by the addition of water and stopping the reaction by vacuum drying is described in U.S. Pat. No. 4,824,664.
Previous methods of providing effervescent compositions rely on mixing powders of acid producing solid and carbonate source. As the mixture disintegrates, particles can separate. Undissolved acid must first dissolve and the acidic solution reach unreacted carbonate to achieve full effervescent. These limitations are overcome and an efficient method of effervescent product manufacture are achieved by using a meltable acid source such as citric acid. Melting said acid around fine particles of carbonate salt provides a more intimate contact for effervescence. Also the melted acid and solid carbonate can be extruded, These and other advantageous features are describe below.
Effervescent products have several advantages. One is to provide carbonate to beverages where the carbon dioxide evolved in acidic solutions stimulates the nose and throat when consumed. The second purpose is facilitate the distribution of soluble materials. A third purpose is to stimulate the suspension of particulate matter. Usually it is sufficient to compress a powdered carbonate salt with a powdered acid forming constituent so that local concentrations of acid mix with the carbonate salt forming carbon dioxide or by providing a final pH of 6.5 or less and concentration of carbonate that exceed the solubility of carbon dioxide in water resulting in carbon dioxide effervescence. Such systems are not compatible with ingredients that may react with the acid-forming component in the presence of moisture. These also are not suitable for components which are reactive and may cause damage to the container in which the tablet is placed. It is the purpose of this invention to provide a means for improving the reaction between the carbonate salt and the acid forming component allowing for an active local effervescence not present with powder mixtures.
It is a further purpose of this invention to provide a means for allowing the inclusion of reactive species.
It is a further purpose of this invention to provide a means for reducing moisture penetration to a moisture sensitive or moisture reactive constituent.
It is a further purpose of this invention to provide a means for reducing air penetration to a oxygen sensitive constituent.
It is a further purpose of this invention to provide for continuous production of dosage forms.
It is a further purpose of this invention to provide for rapid production of dosage forms.
The following terms are described for definition of the specification herein and claims which follow:
xe2x80x9cAqueous solutionxe2x80x9d means any solution containing more than 35% water.
xe2x80x9cMeltable Acidxe2x80x9d means an organic acid which at room temperature is solid which becomes fluid at a temperature below its decomposition point and which when dissolved in an aqueous solution causes the solution to have a pH of less than 6.5.
xe2x80x9cNon-Toxicxe2x80x9d means safe for human or animal consumption at the concentration administered in usual circumstances for a particular product or less than 3% of the lowest mammalian LD50 for components for which toxic effects have not been previously determined.
xe2x80x9cFood gradexe2x80x9d means a food quality standard as defined by US federal standards as suitable for human consumption.
A xe2x80x9cDrying Agentxe2x80x9d means a substance which holds water molecules tightly enough to reduce the reaction rate of other ingredients for which water is a solvent, catalyst or reactant. Anhydrous sodium sulfate is one example.
xe2x80x9cComponent for dissolution or suspensionxe2x80x9d means a solid or liquid comprising one or more ingredients for which it is desired that said ingredients be dissolved or suspended when the effervescent components are dissolved in water thus freeing said entrained ingredients.
A xe2x80x9clow calorie sweetenerxe2x80x9d is one that has sweetness near that of sugar with less and 10% of the caloric value of the equivalent amount of sugar. Aspartame, Acesulfame are examples of synthetic low calorie sweeteners and Acerola cherry extract and stevioside extracted from the stevia plant are examples of natural low calorie sweeteners.
Meltable acids, when heated, and then mixed with carbonate or bicarbonate salt act as moldable plastics, giving a choice of shape of the overall product, rigidity at room temperature, and reduced permeability for contained components and external substances. By combining the carbonate directly with the acid an intimate relationship is established which when the material is dissolved in an aqueous solution provides a much better effervescence than when separate layers are used or when separate particles of acid and carbonate are physically mixed without fusion. Examples of meltable acids are citric acid, malic acid, and oxalic acid. Oxalic acid is toxic because of its binding properties for calcium and therefore is not suitable for use in products to be consumed by animals or humans.
Products which benefit from improved effervescence are those in which carbonation is desired, those in which rapid dissolution is desired and those for which the carbonate-acid mixture prevents contact between the acid and an additional ingredient. Specific examples are: carbonated beverages, bath tablets, effervescent suspended drugs, and oxidative materials, such as calcium hypochlorite which may otherwise react with or interact with the container. Calcium hypochlorite releases chlorine which reacts with paper and other organic materials. Calcium hypochlorite if mixed directly with melted citric acid catches fire! Solid calcium hypochlorite causes spontaneous combustion with many organic compounds with the exception of mineral oil.
Products which benefit from the protective layer of solid acid are those which are subject to oxidative effects, liquids, and those which might otherwise evaporate. Examples of these classes include vitamins, and perfumes.
An example of the extrusion method of effervescent manufacture is a heatable metal pressure chamber with bottom opening and attached valve. Attached to the valve is a die or mold to shape the melted carbonate-acid taffy in the desired form when the valve is opened after the acid has been heated. Continuous molding is a distinct advantage but a batch process is also useful. For the continuous molding method a movable belt or surface is place adjacent to the exit die allowing the extruded material to cool without change in structure. Active cooling of the extruded product may be accomplished by cooling the belt or passing the extruded product through a cold dry chamber.
As a preferred embodiment soluble carbonate salt is mixed with meltable acid in a chamber and as the mixture is extruded in two layers after melting and mixing of the acid with carbonate, components for dissolution or suspension desired for inclusion in the product are placed between two layers resulting in a sandwich covering of the component for dissolution or suspension by the effervescent acid-carbonate mixture. Compressing viscous meltable acid periodically perpendicular to the extrusion direction produces square or rectangular pillow shaped pieces, thereby allowing for controlled dosage of the components for inclusion.
As an additional preferred embodiment said melted acid-carbonate mixture is extruded circumferencially around the component for dissolution or suspension and dosage portions separated by squeezing the melted acid-carbonate thus providing a dosage form in pillow shape. In this case it is necessary that the melted acid-carbonate be thick enough to provide closure at the pillow ends or that the component be introduce to the extrusion process on a controlled, intermittent basis and that the end fusion of the pillow be coordinated so as to compress the melted acid-carbonate between individual component portions.
In another preferred embodiment an effervescent composition is extruded and surrounded by a thin layer of slowly dissolving, water soluble composition and the material shaped by constricting the extrusion at intervals to separate the extrusion into an elongated rod with bullet shaped ends. After separation the rod is cut in half so the center core of effervescent material is exposed. When placed in water the effervescent inner layer produces carbon dioxide gas which caused the rod to move through the water. A preferred example of such a product is one in which sodium or potassium carbonate is mixed with citric acid in a ratio that provides a pH of 4 to 6 when fully dissolved and has sucrose as a surrounding layer. Flavoring and sweetening agent in addition to the sucrose can be added during production of the effervescent core. In another preferred case the sucrose layer is replaced by citric acid and the citric acid is applied in production as a thick melted liquid form. The size of the product is adjusted so that the product can produce an amount of carbonation desired for a carbonated drink of particular volume of water.
When anhydrous citric acid is used for making effervescent products the citric acid remains as a solid after being melted and cooled. By contrast, when citric acid monohydrate is mixed with carbonate salts a small amount of water reacts with the carbonate and a small amount of carbon dioxide is released. When cooled the resulting composite has light weight and rapidly dissolves with effervescence. Effervescent products made with citric acid monohydrate float and provide a means for keeping the composite from settling to the bottom of a vessel containing water.
In a preferred embodiment disinfective products are made using calcium hypochlorite wherein under dry conditions powdered hypochlorite salt is mixed with taffy formed from anhydrous citric acid and sufficient carbonate salt to provide a desired pH and the desired amount of hypochlorite when a finite amount of the composite is dissolved in a particular amount of water.
Example 1 compares small batch preparation of three alkali metal carbonates in the preparation of coated effervescent bath tablets. Two hundred grams of anhydrous citric acid was melted to 125xc2x0 C. then mixed with 150 grams of sodium, or calcium or potassium carbonate. After mixing and while the mixture was still malleable 80 grams in the case of sodium or 40 grams in the case of calcium or potassium of granular calcium hypochlorite was added with mixing. Chlorine vapor originating from this mixing was exhausted. While still in taffy form the mixture was flattened and scored for later cleavage. When cooled individual wafers of effervescent encapsulate calcium hypochlorite were separated and stored in closed containers. Example 1 shows various characteristics of these preparations used to produce chlorine when dissolved in a standard bath tub filled with water.